For diabetes treatment, the blood glucose level of a patient need be maintained in a normal range. Thus, the management of the blood glucose level by the patient himself or herself is important. Particularly, for keeping the blood glucose level in a normal range by insulin injection, measurement of the blood glucose level by the patient himself or herself is essential.
A portable blood glucose level measuring apparatus used for such a purpose is already commercially available, an example of which is disclosed in JP-A-4-357452. This blood glucose level measuring apparatus is used by inserting a disposable test piece provided with an enzyme electrode into a main body. When the test piece is brought into contact with blood as an analyte, a portion of the blood is introduced into a reacting portion by capillary action, thereby generating an anode current due to an enzyme reaction or an electrochemical reaction. In the apparatus, the anode current is converted to a blood glucose level, which is displayed.
In such a measuring apparatus as described above, the analyte, i.e. blood for contact with the test piece is generally sampled using an instrument called lancet as disclosed in JP-A-9-266898 for example. A lancet is a tool used for making a small hole (or making a cut) on the skin of a fingertip, for example, of a patient. The blood drawn from the hole thus formed is brought into contact with a predetermined portion of the test piece. Thus, the self-measurement of the blood glucose level can be performed relatively easily.
However, the conventional self-measurement of the blood glucose level is inconvenient in that the lancet for sampling blood as an analyte is separate from the measuring apparatus, so that the two tools need be carried. Moreover, it is necessary to separately perform the steps of injuring the skin with the lancet and of bringing the blood drawn from the cut into contact with the test piece. Therefore, there is still room for improvement in terms of the convenience of use. Particularly, in bringing the blood into contact with the test piece, a necessary amount of blood need be brought into contact with a predetermined portion of the test piece. Therefore, in the case where this step is performed by an untrained or week-sighted patient or where blood is drawn from an earlobe which cannot be observed by the patient himself or herself, it is not easy to bring the blood drawn from the cut into contact with the test piece quickly and properly.
Further, the test piece is designed to suck blood from a hole at the tip end of the test piece into the biosensor provided in the reacting portion by capillary action. Therefore, 3 to 5 μl of blood need be brought into contact with the test piece to ensure that a necessary amount of blood reaches the reacting portion. If the amount of blood is insufficient or if a sufficient amount of blood is not deposited appropriately on a small area surrounding the tip hole of the test piece, the apparatus may suffer erroneous measurements. In particular, such a case is more likely to occur with respect to patients such as infants and the elderly who tend to suffer insufficient drawing of blood from a cut.
To solve the above-described problems, JP-A-10-28683 proposes a blood glucose level measuring apparatus provided with a lancet. With this apparatus, just by operating the lancet built in the apparatus to injure the skin, the blood drawn from the skin can be measured by a biosensor also built in the apparatus. However, the apparatus disclosed in this gazette still has room for improvement in terms of convenience, because, in use, the lancet needle and the biosensor need be individually set at predetermined positions in the apparatus.
For improving the convenience in use, the inventors of the present invention have proposed, in JP-A-10-166894, a lancet holder which integrates a lancet and a biosensor. According to this apparatus, the patient's action needed for measurement is simplified, thereby enhancing the convenience in use. Further, the reliability of measurement is enhanced while decreasing the amount of analyte necessary for measurement. However, the reliability of measurement with a small amount of analyte of not more than 1.0 μl has not yet been satisfactory.